As computing technology has advanced, the size of computer software applications and the operating systems that run them has grown larger and larger. As the size of the software has increased, so had the demand that is placed on the memory required to support these programs. To deal with the need for an increased number of addressed memory space, the concept of virtual memory was developed. Today, virtually all modern operating systems provide a form of virtual memory to applications.
One newly developed operating system that utilizes virtual memory management is the WINDOWS CE operating system produced by MICROSOFT CORP. WINDOWS CE is a lightweight operating system that is ideal for use in PDAs (Personal Digital Assistants), hand-held computers, palm computers, electronic appliances and the like. WINDOWS CE provides a page-based virtual memory management scheme that allows applications to realize a 32-bit linear address space for four (4) gigabytes (GB) of memory.
A system that utilizes a virtual memory scheme poses a particular problem when the system fails and an attempt is made to debug the system. To debug a system, a software program is used to examine the contents of the system's memory and registers to determine a problem with a system. Debuggers require that a virtual memory-based system that is being debugged be operational because the debugging software at least requires the CPU to execute the software. However, there are situations in which the system is not operational, i.e., the CPU will not execute the debugging code, where it is necessary or desirable to execute debugging code to determine the cause of a system fault. Such a situation arises when using hardware-assisted debugging equipment that completely freezes the system in order to debug it, or when a snapshot of the system is taken to be debugged at a later time (this is referred to as “post-mortem” debugging).
When such a situation arises, it is impossible to rely on the kernel of the operating system to handle a page fault exception to load a missing page when a virtual memory location not currently loaded is accessed for debugging purposes.